The present invention relates to bioabsorbable two-dimensional (2-D) multi-layer composite medical devices and to a method for manufacturing them by spot welding the layers together. The 2-D composites of the present invention can be easily cut into any desirable form by a surgeon during an operation on a patient.
2-D fabric implants are widely used in different medical operations. Both rigid and flexible implants are needed and used in the art. The required properties of such devices vary depending on the application and implantation site. Such applications can be found, for example, in bone fracture, bone augmentation and in other fixation applications, as well as guided tissue regeneration and in soft tissue closure.
However, meshes made of polyglycolic acid and of copolymers of glycolic acid and lactic acid, like DEXON (available from Davis and Geck, USA) and VICRYL (available from Ethicon GmBH, Hamburg Germany) meshes, lose their strength much too fast for many types of surgical applications. Indications of such disadvantageous early degradation include, for example, the development of a disabling gigantic hernia when DEXON mesh is used in an abdominal wall closure. See Nagy K. K., Fildes J. J., Mahr C., Roberts R. R., Krosner S. M., Joseph K. T., Barrett J., Experience with Three Prosthetic Materials in Temporary Abdominal Wall Closure. The American Surgeon, vol. 62, May 1996, pp. 331-335, the entire disclosure of which is incorporated herein by way of this reference. On the other hand, rapidly degrading 2-D fabric devices also have advantages over more slowly degrading or biostable 2-D fabric devices, which advantages include active induction of scar formation. See Rogers F. B., Baumgartner N. E., Robin A. P., Barrett J. A., Absorbable Mesh Splenorrhaphy for Severe Splenic Injuries: Functional Studies In An Animal Model and an Additional Patient Series, Journal of Trauma 31 (2) 1991, pp. 200-204; and Ashammakhi N., Mxc3xa4kelxc3xa4 E. A., Vihtonen K., Rokkanen P., Kuisma H., Txc3x6rmxc3xa4lxc3xa4 P., Strength Retention of Self-reinforced Polyglycolide Membrane: An Experimental Study. Biomaterials 16 (2) 1995, pp. 135-138, the entire disclosures of each of which are incorporated herein by way of this reference.
Also, many biostable (nonresorbable) polymers, polymer blends and elastomers are used as raw materials in manufacturing flexible 2-D fabric implants. However, the use of such materials can cause problems for the patient on a long term basis. One such problem is that loose debris may be released from the implant due to wear, fatigue and/or wearing away of the surrounding tissue environment, which debris may cause chronic inflammation reactions in the patient. See Kossovsky et al., Giant Cell Myocarditis Associated with Silicone, Am J Clin Pathol (1999) 93:148-152; and Rahman et al., Silicone Granulomatous Reactions After First Metarasophalangeal Hemiarthroplasty, Journal of Bone Joint Surgery (1993), 75-B:637-9, the entire disclosures of each of which are incorporated herein by way of this reference. These kinds of implants can also be too stiff and abrasive for tissue and, therefore, result in an unacceptably high rate of fistula formation. See Nagy et al., supra.
The present invention relates to either rigid or flexible bioabsorbable 2-D composite implants and their manufacturing method. These composites can easily be cut into desirable forms by a surgeon during an operation. The composite implant of the invention includes at least two functional layers combined together by a spot welding method, using, e.g., a welding tool whose welding surface contains three-dimensional spots (i.e., points or protuberances emerging from the welding surface). Such welding, performed as described in this patent application, provides the implant of the invention with structural advantages over the prior art sewed implants (which have layers that are attached together by sewing as, e.g., described in U.S. Pat. No. 4,400,833, the entire disclosure of which is incorporated herein by way of this reference). For example, because of the way it is made, the implant of the invention has a surface that is intact and contains no pin holes, through which, for example, body fluids could flow or cells could grow or migrate.
Additional advantages are imparted to the implant of the invention when at least one resorbable film (continuous sheet) component is included in the structure of the implant. In that case, tissue growth through the implant is prevented by the film and, therefore, such devices can be used in applications where separation of two different tissue types for a period of time is essential during the tissue healing period.
The spot welding method of this invention serves to only partially attach together the multiple layers of the laminate composite, at the various points of the spot welding. This partially attached structure provides advantages over the structure of laminate composite implants made from various layers that are completely fixed and compressed onto one another, thereby forming a coherent laminated piece of composite material (e.g., by pressing the layers completely together using heat and pressure). In such completely fixed composites, layered implants, either one or all layers can be severely damaged due to the heat and/or pressure applied to make the implant. For example, the polymeric fibril structures in the layers can lose the initial strength needed for effective function after implantation.
The above disadvantages are overcome by the implant of the present invention, due to its manufacture by spot welding. With the spot welding process of the invention, the fibrillated polymer structures (for example, a mesh) used in making the composite implant of the invention are only partially exposed to heat and pressure at the points of the welding and, therefore, any damage to the implant is localized at those points (spots) of welding. Also, since the laminate layers of the implant of the invention are attached by spot welding, the structure remains more flexible than the prior art compressed, completely fixed, layered implants.
The pattern which the welding tool leaves on the implant can comprise, e.g., groups of lines or welding spots, depending on the configuration and spacing of the welding spots (points) on the welding surface of the tool. Such spots can be either round, oval or angular shaped, or a combination of spot geometries and spacings can be applied. Welding can be performed by applying energy and/or pressure to the welding spots on the welding surface and applying the welding tool to the layers of the composite or by subjecting those layers of the composite to ultrasound, using an ultrasonic welding apparatus with appropriately shaped tool. By varying the materials used and the shape and configuration of the welding tool surface, the properties of the devices can be customized in a wide range.